The present invention relates to a defect inspection apparatus and a defect inspection method, or in particular to a defect inspection apparatus and a defect inspection method using a technique suitable for inspection and analysis of a defect generated on a semiconductor wafer in the process of fabricating a semiconductor electronic circuit, in which an electron beam is radiated on a defective portion and the X-ray spectrum generated is analyzed.
(1) Outline of Defect Analysis by EDX
A method called EDX (Energy Dispersion X-ray Spectrum) is known as a conventional technique for analyzing the cause of the foreign particles generated on a semiconductor wafer during the semiconductor fabrication process. In this EDX method, an electron beam is radiated on a defect on a semiconductor wafer, and the energy dispersion (spectrum) of the X ray generated from a defective portion and the neighborhood thereof is analyzed to estimate the element composition of the foreign particles. Estimating the element composition of foreign particles is very important for specifying the source of the foreign particles and taking a protective measure against dust in the fabrication process.
FIG. 2 is a diagram showing an example of the X-ray spectrum radiated from a defective portion and the neighborhood thereof upon radiation of an electron beam on a defect on a semiconductor wafer. With reference to FIG. 2, an explanation will be given of the fact that an element can be identified by analyzing the X-ray spectrum.
The X-ray spectrum includes a continuous X ray and a characteristic X ray as shown in FIG. 2. The continuous X ray is an electromagnetic wave generated by the incident electron beam accelerated in the direction opposite to the direction of progression when it impinges on an object. The magnitude of energy lost by the impinging electrons is various, with the result that X rays having various energies are radiated. Upon impingement of electrons, the electrons around the atomic nucleus of the wafer obtain energy and are released out of the atomic nucleus. Then, an electron vacancy is formed in the trajectory of the atomic nucleus. The electrons in the outer shell having a higher energy level are trapped in this vacancy, and with the resulting extra energy, a characteristic X ray is generated. The energy level of the electrons is determined by the elements, and therefore the wavelength of the characteristic X ray radiated is determined by the elements. Thus, an element can be identified from the combination of the wavelengths of the characteristic X rays appearing in the spectrum.
The wavelength of the characteristic X ray has been studied for long time, and the wavelength of the characteristic X ray generated by electron transition between different energy levels has already been determined for each element in the periodic table. The conventional EDX analyzer has such a function that the wavelength of the characteristic X ray of each element is stored in a library and the wavelength of the characteristic X ray extracted from the X-ray spectrum is collated with the library thereby to display a corresponding element and the peak position of the spectrum. The user can thus estimate the elements contained in the portion irradiated with the X ray.
(2) Data Acquisition Procedure in EDX
FIG. 3 is a flowchart for explaining the data acquisition procedure for a defective portion in EDX. Now, this data acquisition procedure for the detective portion will be explained. The data acquisition procedure is conducted typically by the operator determining whether or not EDX is to be carried out or not while observing the external appearance of the defective portion of a semiconductor wafer as an image under microscope.
As shown in FIG. 3, the data acquisition for the defective portions is carried out by repeating, for each defect, a series of steps including (1) loading a semiconductor wafer, (2) moving the stage to a defective portion, (3) confirming the external appearance of the defective portion, (4) determining whether EDX is to be carried out or not, and (5) carrying out EDX. As an alternative, in the case where images of defective portions are collected beforehand using an automatic defect reviewing device, the operator confirms the images collected, selects a defective portion to be subjected to EDX, and carries out the EDX detection process for the selected defective portion.
In connection with the foregoing description, a programming method for selecting a defective portion based on the size and type of foreign particles from a list of foreign particles detected by an inspection apparatus is described in JP-A-10-27833, etc.
(3) Protective Measure Based on EDX Data
FIG. 4 is a diagram for explaining a method of estimating the characteristic X ray unique to an element contained in a defect in actual analysis. Now, with reference to FIG. 4, an explanation will be given of a method of estimating the characteristic X ray unique to an element contained in a defect.
In analyzing foreign particles on a product wafer (process wafer), the fact that the X-ray spectrum contains the characteristic X rays generated from the defect or the neighborhood thereof and a lower layer pattern sometimes makes it difficult to estimate the characteristic X ray unique to the element contained in the defect. In actual analysis, therefore, as shown in FIG. 4, for example, the operator detects the X-ray spectrum of the reference portion of an adjoining chip, and by visually comparing the X spectrum of the reference portion with that of the detective portion, estimates the composition of the element contained in the defective portion. Further, the operator estimates the cause of the defect based on the defect composition.
As described above, the operator estimates the composition of the element contained in a defective portion and the cause of the defect by estimating the characteristic X ray unique to the element contained in the defect. In taking a protective measure against the defect, the operator is required to have a sufficient knowledge about the composition of a defect which may occur in each process and each fabrication unit through which a product wafer has been processed. Generally, therefore, it is not easy to estimate the cause of a defect.